The inverse association between relative abundances of oleic acid and arachidonic acid is related to alpha linolenic acid

Background  Many health effects of oils rich in oleic acid seem to be opposite those of arachidonic acid, i.e. concerning cardiovascular risk. In recent studies in humans and in the rat we observed that percentages of OA and AA were inversely related, raising the question of whether the inverse association is a general one, and how it might be explained. In the present work we examine whether percentages of OA and AA are inversely associated in breast muscle lipids of chickens, and whether alpha linolenic acid (ALA) may be related to the OA AA ratio. Methods  The study group consisted of 163 chickens. Breast muscle was collected, and the concentration of fatty acids in muscle lipids was determined using gas chromatography. We studied association between fatty acids using bivariate correlations (Pearson) and linear regression. Synthesis of OA from stearic acid (Stear) was estimated using the OA Stear ratio, and formation of AA from linoleic acid (LA) was estimated by the AA LA ratio. Results  We found a strong inverse relationship between  per cent OA and  per cent  AA in breast muscle lipids of the chickens. There was an inverse association between the OA Stearic acid ratio, estimating Delta9 desaturase, and the AA LA ratio, estimating desaturases elongase activities.  Furthermore, there was a strong negative association between  per cent  AA and the OA Stearic acid ratio, and  per cent  OA correlated negatively with the AA LA ratio. ALA was positively associated with the OA AA ratio, and this association prevailed when controlling for the other fatty acids. ALA was positively associated with the OA Stearic ratio, but was negatively related to the AA LA ratio. Conclusions  The relative abundances of OA and AA that are inversely related in muscle lipids of chickens may be explained by a feedback regulation between the synthesis of OA and AA, and related to ALA, which seems to stimulate formation of OA, and inhibit synthesis of AA, but further studies are required to clarify whether this hypothesis is valid. (Authors abstract)

Although beneficial effects of oils rich in oleic acid have been reported, the mechanisms by which such oils might have beneficial health effects are still incompletely understood. Various antioxidants present in e.g. virgin olive oil, as well as the high content of oleic acid, could partly explain the health effects. An interaction between oleic acid and arachidonic acid was suggested several decades ago in the rat. One mechanism by which OA could counteract those of AA is to reduce the relative abundance of AA in serum and tissues. In the present work data obtained in a previous study was used to extend previous work by examining whether an inverse OA vs. AA association might exist in chickens.  Although a direct feedback regulation between the synthesis of OA and AA seems to be involved to explain the appreciable variation in the OA AA ratio, the possibility exists that this ratio is also governed by other fatty acids. One particular candidate is ALA, the precursor of the endogenous synthesis of EPA, and known to have many health effects. Therefore, as part of the present work an analyses to examine whether ALA might be related to the OA per AA ratio was done. The present work indicates that there is a close inverse relationship between percentages of OA and AA acid in breast muscle lipids of chickens. The result supports previous reports showing a similar inverse relationship between  per cent  OA and  per cent  AA in serum phospholipids of young, healthy subjects, and also found in total serum lipids of rats.   It would appear, therefore, that the observed inverse  per cent OA vs. per cent  AA relationship is a general one.

A tight positive coupling between ALA and the product/precursor estimate used for OA synthesis, as well as a strong negative association between ALA and the AA per LA ratio used to estimate AA synthesis from LA was found. One interpretation of the present results could be that the inverse  OA vs.  per  AA relationship is attributed not only to a direct feedback regulation between the synthesis of this couple of fatty acids, but that ALA, and possibly other fatty acids, may participate to govern the OA vs. AA relationship. Also  preliminary results obtained in total lipids of sera from 36 male rats suggest that ALA is positively correlated with the OA Stearic ratio, and negatively with the AA LA ratio. One explanation of the finding that ALA was positively associated with the OA AA ratio could be that ALA acts as a stimulator of OA synthesis and, or as an inhibitor of AA synthesis.  The product per precursor ratio used in the present study are only crude estimates of enzyme activities, and more direct methods are needed to clarify whether the suggested mechanisms are valid.  It would appear that many of the alleged positive health effects of OA should be expected if OA acts to counteract effects of, or reduces the relative amounts of AA. Furthermore, health effects of ALA have been attributed to the fact that this fatty acid can be converted to EPA. The associations with ALA studied in the present work do not seem, however, to be explained by a similar mechanism.

The diets used for the present study contained 2.4 per cent  linseed oil and had equal n6 n3 ratio, but differed in amount of rendered fat, palm oil, red palm oil, and rapeseed oil. Furthermore, in some subgroups the diets had increased amount of selenium.   Thus, there was a 2 fold variation between diets in the content of palmitic acid, and a 3 fold variation in the content of stearic acid. However, in spite of appreciable differences among the diets, the slope of the association curve between ALA and the OA AA ratio remained unaffected of the diet.

The relative abundances of OA and AA in lipids of chicken breast muscle are inversely related. The results are in agreement with previous findings in man and in the rat, raising the question of whether this relationship is a general one across various species. The results suggest that there might be an inverse coordinated regulation of the formation of the two fatty acids, possibly effected by a feedback regulation between the synthesis of OA and AA, and possibly related to ALA, but further studies are required to clarify whether the hypothesis is valid. (Editors comments)